LONDON (Reuters) - British scientists are developing ways to use nanoparticles as tiny magnets that can heat up and kill cancer cells without harming healthy cells around them.

The researchers have found that iron-oxide nanoparticles can be attached to cancer-seeking antibodies, or injected into cancer-seeking stem cells, which take them straight to the tumours they need to kill.

Heating the cells to just 5 or 6 degrees Celsius above body temperature, in a new device called a magnetic alternating current hyperthermia (MACH) machine, can kill the cancer cells.

The researchers said the MACH device was like a microwave, heating only targeted cells.

"This offers a new way to treat cancer," the team from University College London (UCL) told a briefing on Monday.

"If we get the magnetic particles to migrate to cancer cells, we can kill only the cancer cells, leaving the healthy cells unharmed - the ultimate targeted therapy."

The scientists said the work was at an early stage and no tests had yet been done on humans. They predicted another decade of developing, refining and testing the techniques before they could be licensed to treat cancer.

"We are aiming to be ready to go to clinical trials at the end of three years," said Quentin Pankhurst, professor of physics at UCL.

The scientists said they had already seen the stem cell delivery technique work in mice.

Mark Lythgoe, director of UCL's centre for advanced biomedical imaging, said he and colleagues had shown in a study due to be published soon that certain cells, called mesenchymal stem cells (MSC), when loaded with magnetic nanoparticles, would take them direct to secondary lung tumours, or lung metastases.

"We have now just started the trial where we put those animals into the (MACH) heating system ... to see whether it has killed the lung metastases," he said.

Two other methods were also showing promise, one using cancer-seeking antibodies to carry nanoparticles to head and neck tumours, and another using magnetic fields to steer the tiny magnets to specific parts of the body which need treatment.

"The idea is that we could use these three guided techniques to get the cells to go to the tumour," said Lythgoe. "Then when you've got them there, you put the patient into the MACH system, it heats up the iron oxide particles like a microwave."

Heat is known to kill cancer cells but scientists are seeking ways to target the heat more specifically so healthy cells are not destroyed.

Research presented last month by German scientists showed that heat-treated tumours responded better to chemotherapy, meaning the technique could allow chemotherapy doses to be reduced in the future, reducing toxic side effects.